1. Field of the Invention
The invention relates to processes for removal of turbidity and suspended solids from treated water from water treatment plants, and equipment to carry out the processes. The invention also relates to sewage and waste water dewatering processes and equipment to carry out the processes.
2. Background Art
According to the New Encyclopaedia Britannica, Micropaedia, Volume X, (1974), page 573, describes water purification as treatment consisting of one or more steps by which water is made safe and acceptable for use. Filtration is still the most widely used method of purification. In slow filtration, the water is allowed to pass through a deep layer of fine sand. Most of the impurities are removed by the top inch or two of sand, which is removed and cleaned from time to time or in modern plants is washed in place by special wash water. In rapid filtration plants, the water is treated with a coagulant, such as aluminum sulfate, ferric chloride, or ferric sulfate. This flocculates particles, carrying most suspended matter to the bottom in sedimentation tanks. After this preparation, the water is passed at a relatively rapid rate through small beds of coarse sand that are washed from time to time. Heavily polluted waters may be chlorinated both before and after filtration. Aeration, mixture of air with the water, is carried out if undesirable amounts of iron and manganese are present; they are held in solution in water only in the absence of oxygen.
The New Encyclopaedia Britannica, Macropaedia, Volume 19, (1974), page 651, discusses water treatment plants. Water that has been collected and conveyed to its point of use is treated to make it hygienically safe, attractive, and palatable, and economically suited for its intended uses before it is distributed. The term treatment may refer to a variety of processes, including long-period storage, aeration, coagulation, sedimentation, softening, filtration, disinfection, and other physical and chemical processes in varying combinations, depending primarily on the characteristics of the water source but also on intended use.
Long-period storage of water, which generally means storage in excess of one month, usually takes place in reservoirs or settling basins through which the water passes before it enters the treatment plant proper. Storage reduces suspended sediment and bacteria.
Aeration, the process of mixing air with water, is accomplished by contact bed or spray, cascade, multiple-tray, or air-injection aerators. Spray aerators force water through nozzles into the air. Cascade aerators consist of a series of steps over which the water falls. In multiple-tray aeration, water falls through nozzles in a series of vertically stacked trays. Contact beds are similar to multiple-tray aerators except that the vertically stacked trays are filled with gravel or some other contact media over which the falling water flows. Air-injection units consist of equipment to force small air bubbles through the water. Aeration is used primarily to reduce odors and tastes, to reduce hardness and corrosiveness by removal of carbon dioxide, and to eliminate iron and manganese.
Alum, sodium aluminate, ferrous sulfate with lime, chlorinated copperas, ferric chloride, ferric sulfate, and often other substances are added to the water, to aid coagulation. The addition of coagulants causes the colloidal, color, and mineral particles to agglomerate into a settleable floc. Coagulation is usually accomplished in two stages: rapid mixing of the coagulant with the water and extended slow mixing during which the settleable floc is formed. The floc is then settled out by gravity in settling basins. Coagulation and sedimentation reduce the bacteria content of the water and are particularly effective in reducing color and turbidity, while indirectly reducing odors and tastes. Some coagulants, however, may increase the hardness and corrosiveness of the water.
Softening is the process of removing calcium and magnesium from the water either by chemical precipitation or by ion exchange. The most widely used process is lime-soda softening, in which lime and soda ash are added to the water to cause calcium carbonate and magnesium hydroxide precipitation. Sedimentation follows the addition of chemicals to permit the precipitates to settle. After the addition of lime or lime and soda ash, the softened waters are unstable and require stabilization by recarbonation or other means.
In the ion-exchange process, water is passed through beds of ion-exchange resins or carbonaceous ion-exchange materials. Cation exchangers, which exchange their sodium ions for calcium or magnesium ions in waters, commonly are used. The action is reversible, and the cation exchangers are regenerated periodically with a salt solution. Both water-softening methods are effective, and the lime-soda process also reduces bacteria, turbidity, odors and tastes, and iron and manganese.
Water filtration includes slow-sand filtration, rapid-sand filtration, and microstraining. In slow-sand filtration, low turbidity raw water or settled water is passed directly into beds of fine sand underlain by gravel and an underdrainage system. The sand beds removed suspended matter from the water. Rapid-sand filters allow the water to flow through larger grain sand at much faster rates but are otherwise similar to slow-sand filters. For rapid filters to be effective, prior treatment of the water by coagulation and sedimentation usually is necessary. Rapid-filter beds may be made of silicas and crushed quartz, or crushed anthracite coal. Both slow and rapid filtration reduce color and remove iron and manganese, bacteria, and turbidity. Odor and taste are reduced as an indirect result of rapid-sand filtration. Modern water-treatment plan designs favor rapid-sand filters over slow-sand filters. Both types of filters require periodic cleaning.
Microstraining removes algae and other microparticles from water, usually prior to rapid-sand filtration. Microstraining can greatly increase the length of the rapid-sand filter runs. The microstrainer is a rotating-filter drum covered with a fine stainless-steel mesh having apertures of less than one micron in size. Water passes from the inner section of the unit outward, and the screen is continuously cleaned by a water spray at the top.
Chlorine is most commonly used for the disinfection of water, but ozone and ultraviolet radiation treatment are also used. Chlorine is applied both before filtration, the prechlorination, and as the final water treatment before distribution, the postchlorination. Most large treatment plants use liquid chlorine; usually it is added to the water in amounts that will ensure a small free chlorine residual throughout the water distribution system. Chlorination is effective in destroying bacteria and inactivating viruses as well as in reducing faint odors and tastes in water; but chlorine causes problems by combining chemically with organic compounds. In the presence of intense odors and tastes, chlorination cannot always be employed because it may produce unpleasant tasting by-products.
There are a number of special water-treatment processes in use. Copper sulfate is used for algae control. Activated carbon removes many organic chemicals and odors. Ammonia with chlorine is used for chloramine disinfection and odor control.
Efficiency and dependability are increased in modern water-treatment plants by automation and centralized control. A typical municipal water-treatment plant is shown diagrammatically in FIG. 29.
Since the 1974 articles there have been further development of water purification and water treatment plants.
Recent concerns over safety and trace contaminants in drinking water have driven the development and acceptance of membrane filter technology ranging from micro-filtration, ultra-filtration, nano-filtration, and reverse osmosis in which clarified water is pumped under pressure through large bundles of small diameter (less than 1/10 inch) hollow fibers contained within a collection housing. The fiber bundles are manufactured from a variety of polymeric material, such as, polysulfone or PVDF, which are permeable in the sub-micron range. Permeate (the water which passes through the fiber sidewall) is collected and sent to the distribution system. Reject water (the water and suspended solids, typically less than 0.5 percent, which will not pass through the filter membrane) is discharged as sludge for thickening and dewatering.
Continued increases in demand for potable water has led to the development of ballasted clarification (such as, Kruger's Actific™ process) which utilizes microsand as a seed for floc formation. The microsand provides surface area that enhances flocculation and acts as a ballast or weight. The resulting sand ballasted floc allows for clarifier designs with high flow rates and short retention times, resulting in system configurations that are ⅕ to 1/20 the size of conventional clarifiers. The sludge produced by ballasted flocculation is typically less than 0.1 percent concentration.
Sewage is composed of the liquid and water-carried wastes from residences, commercial buildings, industrial plants, and institutions, together with any groundwater, surface water and storm water which may be present. The terms “wastewater” and “sewage” are sometimes used interchangeably herein.
However, wastewater can be defined as water containing impurities, as suspended solids, resulting from industrial processes.
The composition of sewage depends on its origin and the volume of water in which the wastes are carried. Sewage which originates entirely from residential communities is made up of excreta, bathing and washing water, and kitchen wastes. Other wastes can be present from rural/agricultural sources and/or industrial or commercial establishments.
Modern sewage treatment is generally divided into three phases: primary, secondary, and tertiary. Each of these steps produces sludge, which can be disposed of or used for various purposes.
Primary treatment, or plain sedimentation, removes only the settleable solids from sewage. A modern system for primary treatment entails collecting the sewage, conveying it to a central point for treatment, using both screens to remove large objects and grit chambers to remove grit, and using primary sedimentation tanks to remove the suspended settleable solids. This type of system produces about one third of a gallon of wet sludge per person per day, and facilities for handling and disposing of the sludge are also needed. Primary treatment reduces the concentration of suspended solids by about 60 percent and reduces the BOD (biochemical oxygen demand) by about 35 percent.
Secondary treatment involves the addition of a biological treatment phase following plain sedimentation. At best, this treatment removes about 85 to 95 percent of the organic matter in sewage. It has little effect on dissolved materials or on the nutrients that stimulate the growth of algae in the receiving waters. It also discharges all of the nutrients and dissolved solids, as well as any contaminants which may be added to the water by industrial plants.
There are two basic methods often used in modern secondary treatment, that is, the trickling filter and the activated-sludge processes. In small communities, secondary treatment is sometimes accomplished by either the trickling-filter method or the contact bed method, but usually used is the sand filter method. In larger communities, secondary treatment is generally accomplished by the activated-sludge process.
Sand filters are beds of fine sand, usually 3 feet (1 meter) deep, through which the sewage slowly seeps. As it seeps through the sand, the organic matter is decomposed and stabilized by the microorganisms in the sewage. Sand filters require about 4 acres (1.6 hectares) of sand beds for each thousand people. Because of this large space requirement, sand beds have obvious disadvantages. Also, the time required for the sludge to be formed and dried usually takes weeks. This long drying time means that large surface areas of sand beds have to be used to achieve drying with the attendant large cost of constructing, operating and maintaining the sand beds. Rain adds time to the drying function of sand beds, since the sand beds usually are without any roof or other top covering. Covered sand beds require less area than do uncovered beds but still take weeks to achieve drying and have a higher construction cost. Nowadays, about 90 percent of smaller municipalities use sand beds to dewater sewage coming from primary treatment units. The main purpose of sand beds is the reduction of the water content in the primary-treated sewage.
A contact bed, composed of many layers of stone, slate or other inert material, provides a relatively large surface area for the growth of microorganisms. It operates on a fill-and-draw basis, and the organic matter delivered during the fill period is decomposed by the microorganisms on the bed. The oxygen required by the microorganisms is provided during the resting period, when the bed is exposed to the air.
In the trickling filter system, the sewage is applied to the filter through rotary distributors and, then, is allowed to trickle down over large stone or plastic beds that are covered with microorganisms. The beds are not submerged and, thus, air can reach the organisms at all times. The area requirements for trickling filters are about 5 to 50 acres (2 to 20 hectares) per million people.
In the activated-sludge process, heavy concentrations of aerobic microorganisms, called biological floc or activated sludge, are suspended in the liquid either by agitation which is provided by air which is bubbled into the tank or by mechanical aerators. Final sedimentation tanks are needed to separate the floc material from the flowing liquid. Most of the biologically active sludge, then, is returned to the aeration tank with which to treat the incoming water. The high concentration of active microorganisms which can be maintained in the aeration tank permits the size of the treatment plant to be relatively small, about 1 to 5 acres (0.1 to 2 hectares) per million population.
Tertiary treatment is designed for use in areas either where the degree of treatment must be more than 85 to 95 percent or where the sewage, after treatment, is reused. It is mainly intended to further clean or polish secondary treatment plant effluents by removing additional suspended material and by lowering the BOD, generally by filtration. This polishing, however, has little impact on the dissolved solids, including the nutrients, synthetic organic chemicals, and heavy metals. To eliminate these constituents of sewage, other methods of treatment have been devised. These processes include coagulation and sedimentation, precipitation, adsorption on activated carbon or other adsorbents, foam separation, electrodialysis, reverse osmosis, ion exchange and distillation.
Sludge is the semiliquid mass removed form the liquid flow of sewage. Sludge will vary in amount and characteristics with the characteristics of sewage and plant operation. Sludge from primary treatment is composed of solids usually having a 95 percent moisture content. The accumulated solid materials, or sludge, from sewage treatment processes amount to 50 to 70 pounds (22 to 31 kg) per person per year in the dry state or about one ton (0.9 metric ton) per year in the wet state. Sludge is highly capable of becoming putrid, and can, itself, be a major pollutant if it is not biologically stabilized and disposed of in a suitable manner. Biological stabilization may be accomplished by either aerobic or anaerobic digestion. After digestion, sludge-drying beds are usually used.
In modern sewage treatment plants, mechanical dewatering of sludge by vacuum filters, centrifuges, or other devices is becoming widespread. The dewatered sludge, then, may be heat dried, if it is to be reclaimed, or it may be incinerated. In large communities where large amounts of sludge are produced, mechanical dewatering and incineration are commonly practiced. But there are many smaller communities, rural areas, etc., which have economic constraints and which use the sand bed method to dewater sewage. There is a great need to make the sand bed method more economical by reducing the time for drying waste material (sludge) from the primary-treated sewage effluent and by reducing the time for drying the sludge. Reduced drying time would allow reduction of the size of the sand beds needed.
Early sludge treatment schemes included plain sedimentation, followed by chemical precipitation or sedimentation aided by flocculation chemicals. Chemical precipitation fell into disuse, but may be making a comeback. Nowadays, chemicals are often added to the sewage to promote the coagulation of the finer suspended solids, so that these solids become heavy enough to settle in sedimentation in the primary treatment stage. Typical chemical coagulants in the flocculation of sewage are alum, polymers, ferric sulfate, ferric chloride and lime.
Chlorine is often used to minimize odors from sedimentation tanks and in the final effluent as a disinfectant.
U.S. Pat. No. 5,248,416 (Howard) discloses a sewage treatment system which presents a main flow line and a recirculating line, the former for floc which has appreciated in size due to the addition of a polymer and to passage through an area of agitation/turbulence, and the latter for the return of small sized floc to the agitator/turbulence area for size increase. The passageways of the system include movable flaps which serve recirculation purposes, and a ledge or flutter for current creation and floc build-up. Raw liquid sewage enters the system, whereas the outlet leads to a belt press and/or a dry bed to cake the resulting sludge. More specifically, the apparatus for flocculating fluids containing suspended solids comprises conduit means for conducting the fluid to an outlet in the conduit means. There is means introducing a flock-producing agent into the fluid in the conduit means, a vertical drop mounted ledge means in the vertical drop in the conduit means downstream from the means introducing the flock-producing agent, and a movable mounted ledge means in the vertical drop which serves to increase turbulence and to increase the size of accumulating floc in the fluid. There is a vertical rise in said conduit means, downstream from the vertical drop leading to the outlet. The conduit means includes means connecting the vertical drop to the vertical rise, and there are circulation passageway means connecting the vertical rise to the vertical drop for recirculating smaller size flock to the vertical drop.
In Howard, it is said that a particular feature is that no mixer equipment is required. Polymers are injected into the raw sewage, causing water to separate from the raw sewage during the procedure, resulting in floc build-up. The latter is caused when the polymers begin dissolving with the result that a film of concentrated polymer solution builds up about the polymer particles, forming aggregates or agglomerations, identified as “flocks”. Turbulence is a key factor, where such is said to be accomplished through a ledge (which flutters) located in the vertical drop conduit and a series of movable flaps disposed within the recirculating conduit. The singular stated purpose of the Howard scheme is to create flock, i.e., solids with a minimum of water content, through separation. Restated otherwise, the Howard scheme, through turbulence or tumbler-mixer action, is said to create additional floc (of a larger size) which goes to output, whereas smaller floc is caused to recirculate said increase, thereby, in size for repeated passage to output.
The Sarasota, Fla. Public Utility Company purchased one vacuumed assist drying bed from USEP (Company). The process consisted of walls, concrete floor with grooves, and a sealed down porous block tile consisting of small stones with epoxy to hold together with a smaller granular material on top. The grooves were used to collect the water when the vacuum was applied. This is similar to the surface of a cement building block. As the utility scraped sludge from the surface, the tiles wore down to the stone and some were completely removed. A thin layer of small stone was placed to level out the bed. A GeoWeb stabilization material was placed directly on the original plates and placed stone. Sand filled the stabilization material and several inches above. By installing the stabilization material and sand the utility vehicle was able to drive on the beds. The beds were decommissioned in 1996. (See FIGS. 27 and 28.)
U.S. Pat. Nos. 6,051,137, 5,770,056, 5,660,733, 5,683,583, 5,725,766 and 5,611,921 disclose a process of dewatering treated sewage, and equipment and installation used therein or therewith. Such process is usually referred herein as the previous Deskins process-scheme. The previous Deskins process-scheme includes mixing the sewage with a coagulant or flocculant aid, usually activated polymer. The sewage is then mixed and flocculated at conditions which involved extensive mixing turbulence of the sewage and whereby part of the sewage is recycled so as to be again subjected to such mixing and flocculating. Flocks form the solid particles in the sewage. The pH of the sewage is chemically adjusted into the basic pH range or to a higher basic pH. The sewage is applied to a sand bed whereby the flocculated solids in the sewage are separated from the liquid in the sewage, by collecting on the top of the sand bed. The flocculated solids located on the top of the sand bed are air dried. The dried flocculated solids are removed from the top of the sand bed.
The first step/stage in the previous Deskins process-scheme used an inline polymer mixing-feeding (injection) system to incorporate activated polymer into the sewage flow line (see FIG. 25). The inline polymer preparation system eliminated this need for batching tanks, mixers and polymer transfer pumps. The inline polymer system could be a conventional one or an inline polymer mixing-feeding system of the previous Deskins process-scheme. The inline polymer system (chemical pump) of activated precise amounts of neat polymer and water, then metered the fully activated stock solution to the point of use without the need of transfer pumps.
The polymer is an emulsification of long chain organic polymer in oil. The water and mixing opens up of uncoils the polymer to expose charge sites in the polymer chain.
Coagulants or flocculants, such as, alum. ferric sulfate, ferric sulfate, ferric chloride and lime, could be used in place of the activated polymer in the sewage flow line to coagulate or flocculate the solids in the sewage. These coagulants or flocculants cause formation of an insoluble precipitate which adsorbs colloidal and suspended solids.
The second step/stage in the previous Deskins process-scheme used an inline mixing flocculator (see FIG. 24). An inline mixing-flocculating device was used to enhance the chemically induced liquid-solids separation in the sludge dewatering process utilized at most wastewater treatment plants. The flocculator was used in any type of mechanical dewatering scheme that used a chemical as a coagulant or flocculant aid. The overall output and efficiency of the dewatering process was greatly increased by the thoroughness of the flocculating process. Prior art sludge production normally was 14,000 to 16,000 gallons of dewatered sludge per gallon of polymer; the mixer-flocculator unit provided a reduction of 40 to 60 percent in polymer consumption.
The third step/stage in the previous Deskins process-scheme was a chemical induced pH adjustment of the sewage exiting the mixer-flocculating system. Liquid caustic, lime or other suitable base was injected into the discharge side of the mixer-flocculator unit and the temperature of the water to the inline polymer system was increased, thereby increasing the liquid/solids pH balance.
As the liquid/solids content exited the inline mixer-flocculator unit, an electronic driven diaphragm pump or gear driven pump pumped liquid caustic or lime into the discharge line of the flocculator-mixer unit. The pH of the sludge was increased to 12 by the chemical. The pH of the sludge remained at 12 for 72 hours, and, during this period of time, the temperature reached 52° C. and remained at that temperature for at least 12 hours. At the end of the 72 hours period during which the pH of the sludge was above 12, the sludge could then be air dried to achieve a percent solids of greater than 50 percent. The liquid caustic or lime pump could be present on a transportable dewatering trailer with the mixer-flocculating system and the polymer feed system and, thus, was easily transported.
The fourth step/stage in the previous Deskins process-scheme used a sand grid cell in a sand bed used for dewatering sludge (see FIG. 1). The sand-cell was grid used to stabilize filtration media in any new or existing sand drying bed. It was preferably manufactured of heavy-duty polyethylene. Preferably the sand grid was honeycomb shaped or similar shaped. The fixed media (i.e., grid) was best installed in the filtration sand about six inches below the surface. Under load, the sand-cell generated powerful lateral confinement forces and sand-to-cell or stone-to-cell frictions. This process created a bridging with high flexural strength and stiffness. The sand-cell greatly enhanced the dewatering process. Plant operators could drive an end or front loader or tractor over the entire bed thereby significantly reducing cleaning time and eliminating expensive manual labor. Surface and subsurface bed stabilization was achieved using the invention grid. This allowed for excellent manueverability of equipment, eliminated surface and subsurface, compaction of the sand media and produced an excellent drainage environment, and 100 percent saturation and drainage within about 10 minutes from start to pouring of the sewage resulted from the use of the grid.
This step of the previous Deskins process-scheme involved use of a sand-cell media to stabilize filtration sand/media in any new or existing sand drying bed (best constructed of concrete).
A standard sand-cell section could have nominal dimensions of eight feet wide by twenty feet long by six inches deep. However, a standard sand-cell section could have any length, width and height to fully fit into the dimensions of the sand cell in case. All of the individual sand-cells forming a sand-cell section, generally, were uniform in shape and size. Preferably, the individual sand-cells were about 6 inches wide, 6 inches long, about 6 inches deep, hexagonal in shape and, together, formed a honeycomb. The honeycomb is one of the strongest, yet lightest, shapes found in nature. A standard sand-cell section could be made from high-density polyethylene plastic, any other suitable plastic or resin, stainless steel, fiberglass, concrete, wood, or any other suitable metal or material, or any form of fabricated steel, preferably high-density polyethylene plastic.
The sand-cell media was advantageously installed in the filtration sand or stone with its top surface most preferably about six inches, preferably not more than 12 inches or less than 2 inches, below its surface of the sand. Under load, the sand-cell media generates powerful lateral confinement forces and stone or sand to cell frictions. This process created a bridging with high flexural strength and stiffness.
The benefits of using sand-cell media were stated to be numerous. A subsurface which includes sand-cell media does not compact which allows the free water to pass quickly through the media. The high flexural strength and stiffness of a subsurface which includes sand-cell media allowed equipment such as end loaders to drive directly onto the entire sludge drying bed without destroying the integrity of the filtration sand. This, in turn, significantly reduced the loading and cleaning time, and eliminated expensive manual labor. Other benefits of using the sand-cell media were stated to include: lateral slippage or shear of the filtration media was prevented; filtration media replacement costs were reduced; economical standard washed sand or “P” gravel for rapid dewatering could be used (as opposed to conventional drying bed materials); square foot installation costs were reduced by ninety-four percent over the fixed media system; and total maintenance costs were reduced by more than seventy-five percent.
With regard to the previous Deskins process-scheme of FIG. 1, Enclosure 849 contains a sand bed. Onto layer of non-porous material (850), e.g., concrete, a layer of porous material (853) is positioned. Porous material (853) is used as a filter media and usually stone, crushed rock, ceramic shapes, slag and plastics of 1 to 6 inches, practically 2 to 4 inches, in size are used. Stones or pebbles are preferred. At least one—usually more than one—projection of porous material (854) extends from the porous layer (853) into the layer of non-porous material (850). Embedded in each projection channels (848) in porous material (854) is at least one non-porous pipe (855) having at least one hole into which liquid can drain. A layer of sand (857) is positioned above the layer of porous materials (853). The sand-cell media sections (865) are positioned above this layer of sand (857). Sand is located in the passageways in the sand cell grid. Above each sand-cell media section (865) is placed in a layer of sand (861). This layer of sand (861) is usually, though not necessarily, at least six inches in depth.
Walls (851) surround on all four sides of an area having one or more sand-cell media sections. One wall (851) is shorter to allow a front loader or the like into the enclosure. Each surrounding, dividing wall (851) extends upward from one or more footing supports (852) which are positioned, at least partially, in the layer of non-porous material (850). The top of each dividing wall (851) extends above the layer of sand (861) overlaying the sand-cell media section(s). On the top of each dividing wall (851), which runs between two enclosure areas having the sand-cell media sections, is a portable nozzle which is used to pour sewage into the enclosures.
Each sand-cell media section (865) is made up of one or more sand-cells (858) having the same shape and size. Typically, the sand-cell media section (865) is made up of honeycomb-shaped sand-cells (858) which are joined together in a honeycomb formation (i.e., each sand-cell which is not in an outer layer, where it intersects another sand-cell, it intersects three other sand-cells) channel runs through the interior of each sand-cell.
Sewage is poured through the channel into one or more enclosures (849) for the sand beds. The liquid permeates the outer sand layer, flows through the sand in the channels in the grid (865) in the centers of the sand-cells, permeates the layer of sand beneath the sand-cell media and permeates the pebble layer beneath the layer, leaving the collected sludge solids on top of the outer sand-layer to dry from the sun and air.
The fifth step/stage in the previous Deskins process-scheme used a sludge retriever (see FIG. 13) to separate the dried sludge layer from the sand in the sand bed. The sludge retriever was designed to fit any adequately rated (front-end) loader and was powered by the hydraulic system of the loader. Easily operated by one person, the retriever's rotary drum of the efficiently broke up (chops) solid waste and propelled it into a hopper. The sludge was chopped into very small granular particles, enhancing transportation and handling cost. The unique combing action of the rotating drum (preferably having 3-inch adjustable tines) not only removed sludge without significantly disturbing the filtering sand, it also leveled the bed surface to promote uniform drying. Each bucketload of sludge removed by the sludge retriever usually only yielded an insignificant amount of sand for precision sludge clean-up. The sludge retriever (automated) made sludge removal and drying bed preparation a one-man, one-machine operation. It also leveled and aerated the sand bed for the next pouring of sewage into the sand bed.
The sludge removal attachment was capable of removing dried wastewater sludge from sand drying beds. The implement was also capable of being attached to a front end loader. The mechanism had, for example, a two cubic yard bucket, constructed of ¼ inch steel, and a shaft-type rotary drum having multiple three inch tines. The unit was furnished with an expanded steel cover for the rotor and bucket. Rotor end plates were ½ inch steel minimum. The rotary action of the drum accomplished several functions. First, it removed the sludge layer. Second, it simultaneously leveled the surface of the drying bed. Third, by reversing the direction of the rotary drum, the sand bed could be aerated to a depth of three inches. Basically, the sludge was removed by passing the unit over the drying bed and sweeping up the dried sludge.
Alternatively, the sludge removal attachment (retriever) was capable of removing air-dried wastewater sludge from the sand bed. The unit was a bucket or scoop type device. Sludge was removed by passing the unit over the drying bed and scooping up the dried sludge.
Referring to FIG. 36, a previous waste water treatment installation of Deskins is shown. The installation used a sloped trench. There was a shallow rock in the given area and the engineer was trying to prevent a lot of blasting. We maintained a trench however shallow and 3 layers of stone. The third layer from the bottom housing the panels with 6 inch of sand on top.